Broadband optics for manipulating light beams and images

ABSTRACT

The objective of the present invention is providing optical systems for controlling with propagation of light beams in lateral and angular space, and through optical apertures. Said light beams include laser beams as well as beams with wide spectrum of wavelengths and large divergence angles. Said optical systems are based on combination of diffractive waveplates with diffractive properties that can be controlled with the aid of external stimuli such as electrical fields, temperature, optical beams and mechanical means.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/697,083, filed Jan. 29, 2010 and entitled “BROADBAND OPTICS FORMANIPULATING LIGHT BEAMS AND IMAGES”.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with Government support under Contract No.W911QY-07-C-0032.

RIGHTS OF THE GOVERNMENT

The invention described herein may be manufactured and used by or forthe Government of the United States for all governmental purposeswithout the payment of any royalty.

FIELD OF THE INVENTION

This invention relates to optical beam control and, in particular, tomethods, systems, apparatus and devices for manipulating with lightbeams, including laser beams and beams with wide spectra and divergenceangles, by translating them in the lateral direction and varying theirpropagation direction over large angles for optical switching, beamscanning, spectral modulation, optical tweezers, thermal seeker,imaging, information displays, and other photonics applications.

BACKGROUND OF THE INVENTION

The present invention relates to optical systems for controlling withpropagation of light beams. Pointing and positioning systems areenabling components for most laser applications. Conventionally, this isaccomplished using mirrors, scan wheels, optical wedges, and othertwo-axis gimbal arrangements as exemplified, for example, in the U.S.Pat. No. 7,319,566 to Prince et al. These opto-mechanical systems arecomplex, bulky and heavy for large area beams. For example, the prismapex angle, hence its thickness is increased to achieve largerdeflection angles. The electromechanical systems for rotation,translation or oscillation of such mirrors, prisms, and other opticalcomponents require high electrical power for their operation. They arerelatively slow and have limited range of angles that could be coveredwithin given time period.

Thus, there is a need for thin, light-weight, fast, and inexpensivepointing, positioning, and switching systems for light beams,particularly, for laser beams. The state-of-the-art developments includeall-electronics systems and rotating diffraction gratings. Theall-electronics systems with no moving parts, as reviewed in P. F.McManamon, P. J. Bos, M. J. Escuti, J. Heikenfeld, S. Serati, H. Xie, E.A. Watson, A Review of Phased Array Steering for Narrow-BandElectrooptical Systems, Proceedings of the IEEE, Vol. 97, pages1078-1096 (2009), require a large number of high efficiency diffractiongratings and spatial light modulators and/or electrically controlledwaveplates. As a result, the overall transmission of these systems isreduced along with their radiation damage threshold, and their speed islimited by the liquid crystal spatial light modulators and variableretarders.

Rotating diffraction gratings as described in J. C. Wyant, “Rotatingdiffraction grating laser beam scanner,” Applied Optics, 14, pages1057-1058 (1975), and in the U.S. Pat. No. 3,721,486 to Bramley,partially solves the problem of obtaining larger diffraction angle inthinner optical system, compared, for example to the system of Risleyprisms. The light beam diffracted by the first grating in the path ofthe beam is further diffracted by the second grating. Depending onorientation of those gratings with respect to each other, the deflectionangle of the beam can thus be varied between nearly 0 to double of thediffraction angle exhibited by a single grating. The problem with suchsystems is that phase gratings typically diffract light into multipleorders that need to be blocked along with the 0^(th) order beam. Highefficiency Bragg type gratings have narrow spectral and angular range asdescribed in the U.S. Pat. No. 7,324,286 to Glebov et al., and can beused practically for laser beams only, expanded and collimated tominimize divergence. Blazed gratings such as proposed in the U.S. Pat.No. 6,792,028 to Cook et al., still exhibit a multitude of diffractionorders due to their discontinuous structure and do not improveconsiderably on angular selectivity and efficiency.

The cycloidal diffractive waveplates (DWs), essentially, anisotropicplates meeting half-wave condition but with optical axis orientationrotating in the plane of the waveplate in a cycloidal manner, asdescribed in the review S. R. Nersisyan, N. Y. Tabiryan, D. M. Steeves,B. R. Kimball, “Optical Axis Gratings in Liquid Crystals and their usefor Polarization insensitive optical switching,” J. Nonlinear Opt. Phys.& Mat., 18, 1-47 (2009), do not have the disadvantages of conventionalphase gratings. Moreover, DWs, referred to also as optical axis gratingsand polarization gratings, can provide nearly 100% diffractionefficiency in micrometer thin layers. Furthermore, due to theirwaveplate nature, their diffraction spectrum is broadband, and can evenbe made practically achromatic. Due to their thinness and hightransparency, they can be used in high power laser systems.

Thus, replacing Risley prisms, wedges, mirrors and/or phase gratingswith DW s, provides many advantages for manipulating with light beamsand imaging. As shown in S. R. Nersisyan, N. Y. Tabiryan, L. Hoke, D. M.Steeves, B. Kimball, Polarization insensitive imaging throughpolarization gratings, Optics Express, 17, 1817-1830 (2009), not onlylaser beams, but complex images can be steered over large angles withoutlight attenuation or image deformation. That paper further showed thatutilizing a pair of closely spaced DWs, one of them with switchablecharacteristics, it is possible to manipulate with transmission ofunpolarized beams and images. This concept suggested and demonstrated inS. R. Nersisyan, N. Y. Tabiryan, L. Hoke, D. M. Steeves, B. Kimball,“Polarization insensitive imaging through polarization gratings,” OpticsExpress, 17, 1817-1830 (2009) was subsequently cited and tested in C.Oh, J. Kim, J. P. Muth, M. Escuti, “A new beam steering concept: Riesleygratings,” Proc. SPIE, vol. 7466, pp. 74660J1-J8 (2009).

BRIEF SUMMARY OF THE INVENTION

Thus, the objective of the present invention is providing means forswitching and manipulating with light beams and images in lateral andangular space using a set of DW s capable of deflecting nearly 100% oflight using thin material layers for a broad band of wavelengths anddivergence angles.

The second objective of the present invention is incorporating in saidset DWs with controlled characteristics of their optical properties forfurther enhancing optical manipulation capabilities of said systems.

A further objective of the present invention is providing opticalsystems, incorporating said DW set, wherein manipulation of light andimages with the DW set is transformed into transmission modulation of atthe output of the optical system.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1A schematically shows deflection of a circularly polarized lightbeam with a pair of diffractive waveplates.

FIG. 1B schematically shows the structure of diffractive waveplates atdifferent rotational positions.

FIG. 2A shows sample dependence of the propagation angle of a light beamat the output of a pair of diffractive waveplates as a function of therotational position between the waveplates.

FIG. 2B demonstrates the capability of a pair of diffractive waveplatesto steer with no distortions complex images carried by an unpolarizedlight.

FIG. 3A schematically shows the displacement of a light beam by a pairof diffractive waveplates with parallel orientation of their opticalaxis modulation directions.

FIG. 3B schematically shows the increase in the resultant deflectionangle of a light beam by a pair of diffractive waveplates withanti-parallel orientation of their optical axis modulation directions.

FIG. 3C shows the optical axis orientation pattern in diffractivewaveplates with antiparallel orientation of their optical axismodulation directions.

FIG. 4A schematically shows increasing of the deflection angle of alight beam by a set of four diffractive waveplates each arrangedanti-parallel with respect to the previous one.

FIG. 4B demonstrates increasing deflection angle of a light beam byincreasing the number of diffractive waveplates from one to four, andcomparing them to the original propagation direction of the beam.

FIG. 5 shows increasing deflection angle of a light beam by a system ofdiffractive waveplates tilted with respect to each other.

FIG. 6A and B schematically show switching between transmittive anddeflective states of a pair of diffractive waveplates when switching oneof the diffractive waveplates into an optically homogeneousnon-diffractive state shown in C.

FIG. 7 shows a schematic of a beam combining function of a pair ofdiffractive waveplates.

FIG. 8A, Band C show a schematic of a system for controlling thespectrum of a light beam with the aid of a set of diffractivewaveplates.

DETAILED DESCRIPTION OF THE INVENTION

Before explaining the disclosed embodiment of the present invention indetail it is to be understood that the invention is not limited in itsapplication to the details of the particular arrangement shown since theinvention is capable of other embodiments. Also, the terminology usedherein is for the purpose of description and not limitation.

The preferred embodiment of the present invention includes two DWs,marked with numerals 103 and 105 in FIG. 1A, arranged parallel to eachother in close proximity. At the output of the system of DWs 103 and105, the pointing direction of the light beam 108, circularly polarizedas shown by spirals 102 and 107, is, in general, different from that ofthe propagation direction of the light beam 101 incident on the system,controlled with relative rotational positions of the DWs asschematically shown by arrows 104 and 106. The optical axis orientationpattern corresponding to different rotational positions of said DWs isshown in FIG. 1B wherein the axes of elongated ellipses 109 correspondto local optical axis orientation direction. In the preferredembodiment, DWs are made of liquid crystal polymers though otheroptically anisotropic materials and material structures such assubwavelength gratings can be used as well. In general, the layer of DW,typically only a few micrometer thick, is coated on a substrate 110 forstability and robustness. The substrate can be made of a materialadequate for the particular application. As an example, a fused silicacan be used when controlling UV light beams, and highly transparentglass materials with low absorption can be used for controlling highpower laser beams.

The plot of output angles measured for a sample system as a function ofangular position between the DWs in S. R. Nersisyan, N. Y. Tabiryan, L.Hoke, D. M. Steeves, B. Kimball, “Polarization insensitive imagingthrough polarization gratings,” Optics Express, 17 (3), 1817-1830 (2009)is shown in FIG. 2A for normal incidence of the beam on the first DW. Inthe setup shown in FIG. 1A, the polarization of the incident beam isassumed circular, as schematically shown by the spiral 102. The outputbeam 108 in this case maintains the circular polarization state 107. Incase of incident unpolarized or linearly polarized beam, two beams oforthogonal circular polarization are generated at the output of thesystem of two DWs, and the angle between them changes from nearly 0 tonearly double of the diffraction angle depending on relative rotationalpositions between the DWs as shown in FIG. 2B for light beam carrying acomplex image. No image distortions occurs in this process.

Increasing the distance Δz between two identical DWs 302 and 304, FIG.3, introduces transverse shift Δx of the beam 305 emerging from thesystem with respect to the position of the input beam 301 as a result ofdeflection of the beam by the first DW 302. Said emerging beam 305propagates parallel to the input beam 301 in case the optical axismodulation directions of DW s 302 and 304 are parallel, FIG. 3A, and italso changes in propagation direction when the DW 304 is rotated withrespect to DW 302 into a new position 306, FIG. 3B. The overalldeflection angle of the beam can be maximized positioning the output DW306 anti-parallel with respect to the input DW 302. The optical axisalignment patterns for anti-parallel DWs 302 and 306 are schematicallyshown in FIG. 3C. The beam can be steered over arbitrarily large anglesby adding DWs into the system. Four DWs, 406-409, are shown in FIG. 4Aas an example. The input light 401 undergoes four deflections, 402-405.In order for each subsequent deflection to further increase theresultant deflection angle, the DWs 407 and 409 have to be arrangedanti-parallel to DWs 406 and 408. A demonstration of light deflection bysuch a system of four DWs is shown in FIG. 4B. In general, DWs can betilted with respect to each other such as each of the subsequent DWs isnearly perpendicular to the beam deflected by the previous DW. The DWs507 and 509 are anti-parallel to the DWs 506 and 508, and all fourdeflected beam 502-505 of the input beam 501 result in increasing totaldeflection angle.

In another embodiment, one or more DWs in a system can be switchedbetween diffractive and non-diffractive states, optically, thermally,electrically, mechanically, or by any other means, due the effect ofexternal stimuli on optical anisotropy and optical axis orientationmodulation pattern. For example, the DW can be made of azobenzene liquidcrystal polymer that can be transformed into isotropic state orrealigned by light beams as discussed in S. R. Nersisyan, N. Y.Tabiryan, D. M. Steeves, B. R. Kimball, “Optical Axis Gratings in LiquidCrystals and their use for Polarization insensitive optical switching,”J. Nonlinear Opt. Phys. & Mat., 18, 1-47 (2009). Alternatively, DWs canbe transformed into homogeneous orientation state by electrical fieldsif they are made of liquid crystals or liquid crystal polymer networkmaterials.

Particularly important is the case shown in FIG. 6 when a DW 603 with afixed diffractive property is paired with a controllable DW 602 inconfiguration when their optical axis modulation directions areparallel. As noted in S. R. Nersisyan, N. Y. Tabiryan, L. Hoke, D. M.Steeves, B. Kimball, “Polarization insensitive imaging throughpolarization gratings,” Optics Express, 17 (3), 1817-1830 (2009), thisstate corresponds to total cancellation of diffraction, and such a pairallows transmitting the light beam 601 through the system as shownschematically in FIG. 6A. An image sensor 604 furnished with an aperture605 large enough not to block the transmitted beam would not registerany distortions to the beam. In case the DW 602 is transformed into anon-diffractive state 606, the diffraction of, generally, an unpolarizedlight on the remaining DW 603 redirects the input beam 601 intodiffracted beams 607 and 608 as shown in FIG. 6B, diffracting it intoorthogonal circular polarized components in case of unpolarized orlinearly polarized incident beam. No beam is acting on an image sensor604 in this case provided the deflected beams propagate beyond thereceiving aperture of the image sensor. Thus, the system described inFIG. 6 undergoes switching from high transmission to no orlow-transmission state as a result of switching the structure of one ofthe DWs in the system from diffractive state 603 into a non-diffractivestate 606, FIG. 6C. Indeed, such change in transmission throughparticular aperture can be obtained also by mechanically changing therotational position of the DWs or the distance between them.

Paired DWs and their systems can have many applications in photonics. Asetup for beam combining is shown in FIG. 7. Two parallel propagatinglight beams of orthogonal circular polarizations 701 and 704, afterbeing deflected by the first DW 707 are further deflected into beams 702and 705, emerging as overlapping beams of the same propagation direction703 and 706 by the second DW 707 in FIG. 7.

Given the thinness of individual DW layers, a multilayer system can bedesigned for spectrally selective switching without compromising thehigh throughput and the small size of the system. In the embodimentshown in FIG. 8, a set of DW pairs is used for controlling with thespectral content of the transmitted light by allowing light at differentportions of the spectrum at least partially be deflected out of thesystem. The beams 801 and 804 in FIG. 8 are assumed to possess withdifferent, non-overlapping, spectral content. The individual DWs in thefirst pair 807 are optimized for diffracting the light beam 801 whilehaving diffraction spectrum out of the spectral range of the beam 804.The individual DWs in the second pair 808 are optimized for diffractingthe light beam 804 while having diffraction spectrum out of the spectralrange of the beam 801. Thus, when DWs in both pairs are parallel alignedwith respect to their optical axis modulation direction, all the lightis transmitted, and the spectral content of the output light is the sameas in the input light. In this case shown in FIG. SA, the input light801 propagates through the first DW pair into the beam 802 withoutchanging its propagation direction due to diffraction on both DWsconstituting the pair 807. The beam 802 further propagates through thesecond DW pair 808 into the beam 803 without deflection since itsspectrum is out of the diffraction spectrum of the second DW pair 808.Similarly, the input light 804 propagates through the first DW pair intothe beam 805 without changing its propagation direction since itsspectrum is out of the diffraction spectrum of the first DW pair 807.The beam 805 further propagates through the second DW pair 808 into thebeam 806 due to the diffraction on both DWs constituting the pair 808.

In case one of the DWs constituting the first pair 807 is switched intonondiffractive state 809, or is rotated to double the diffraction angleof the beam 801 by the first DW in the pair 807, the beam 801 isdiffracted out of the optical system into a beam 810. Propagation of thebeam 804 is not affected by that. Thus the light spectrum obtained atthe output of the optical system coincides with that of the beam 804,FIG. 8B.

In case one of the DWs constituting the second pair 808 is switched intonondiffractive state 811, or is rotated to double the diffraction angleof the beam 805 by the first DW in the pair 808, the beam 805 isdiffracted out of the optical system into a beam 812. Propagation of thebeam 802 is not affected by that. Thus the light spectrum obtained atthe output of the optical system coincides with that of the beam 801,FIG. 8C.

Although the present invention has been described above by way of apreferred embodiment, this embodiment can be modified at will, withinthe scope of the appended claims, without departing from the spirit andnature of the subject invention.

1-11. (canceled)
 12. A system for positioning light beams comprising:(a) a light source irradiating a light beam; (b) a plurality ofdiffractive waveplates configured to receive and diffract the lightbeam; (c) means for independently controlling one or more diffractiveproperties of one or more of the plurality of diffractive waveplates.13. The system of claim 12 further comprising means for shaping thelight beam via controlling one or more of divergence, spectral content,polarization and profile.
 14. The system of claim 12 wherein theplurality of diffractive waveplates comprises at least one pair ofoptically identical diffractive waveplates.
 15. The system as in claim12 wherein the means for independently controlling one or morediffractive properties of one or more of the plurality of diffractivewaveplates comprises varying one or more of electric field, magneticfield, optical radiation, temperature and mechanical stress.
 16. Thesystem of claim 15 wherein the plurality of diffractive waveplates isdeposited sequentially on the same substrate.
 17. The system of claim 12wherein the means for independently controlling one or more diffractiveproperties of one or more of the plurality of diffractive waveplatescomprises varying one or more of temperature, mechanical rotationassembly and mechanical displacement assembly.
 18. The system of claim12 wherein the light beam is produced by a laser source withquasi-monochromatic spectrum.
 19. The system of claim 12 wherein thelight beam is produced by a source with broadband angular spectrum. 20.The system of claim 12 wherein the diffractive waveplates deflect lightwith nearly 100% efficiency in a broad spectrum of wavelengths.
 21. Thesystem of claim 19 wherein the light beam is produced by a source withbroadband wavelength spectrum.
 22. The system of claim 12 furthercomprising an optical setup for receiving and controlling lightirradiated by the light source and emanating at the output of theplurality of diffractive waveplates, said optical setup including one ormore of spatial filters, spectral filters, polarizers and diffractiongratings.